Electric power steering (EPS) systems have been the subject of development by auto manufacturers and suppliers for over a decade because of its fuel economy and ease-of-control advantages compared with traditional steering systems, such as hydraulic power steering (HPS) systems. These EPS systems reduce the effort required to control a vehicle by sensing an input from a vehicle operator, via a steering wheel, and generating a torque command that transmits a force to a steering gear assembly thus aiding the vehicle operator in controlling the vehicle. However, some potential problems may arise because the input of the EPS system into the steering action has a direct affect on the driver feel or feedback from the road wheel. As a consequence, any error in the hardware and/or software of the EPS system directly affects driver control of the vehicle.
Thus, because EPS systems are at the heart of vehicle control, vehicle safety standards outlining acceptable EPS system operational guidelines have been developed in order to prevent or minimize potential vehicular accidents that may be caused by any EPS system errors or failures that may occur. As a result of these guidelines, vehicle level safety requirements have been established that promulgate thresholds for allowable errors in the torque commands generated by an EPS system.
Referring to FIG. 1, a graph 200 representing an example of vehicle level safety requirement standards is shown. These requirements, which are commonly expressed as a function of an allowable torque error per event time, takes the form of an allowable steady state value for a relatively infinite amount of time and a progressively increasing allowable error for shorter time durations. For an EPS system to be able to handle errors in the system hardware and/or software, the EPS system may have a diagnostic and/or regulatory capability that senses when an error has occurred, that diagnoses and determines what corrective action is required and that performs this corrective action to limit these errors to be within the requirements established by vehicle safety standards. In addition, external commands may also be used to communicate actions or problems to the EPS system, such as a vehicle stability augmentation signal sent to a vehicle steering system from a brake controller, where little is known about the brake software or communications. Although this diagnostic and regulatory capability currently exists, a great deal of hardware and/or software resources must be consumed in order to perform this task, increasing system cost, size and complexity.
In many cases, such as where restricting the steady state/DC value of the signal is acceptable, the EPS system error requirements established by vehicle safety standards may be met by implementing a firewall approach, whereby a series of checks are employed to ensure that the torque commands reaching the firewall are limited to a maximum safe value. Current design techniques limit this maximum value to the steady state value 202 shown in FIG. 1. Although this approach works well for relatively steady state signals, it is not very effective for signals that operate within the transient portion 204 of the graph shown in FIG. 1, thus requiring designers to sacrifice EPS system performance in order to limit this transient portion 204 to be within the steady state value 202.
A method for conforming an input signal to vehicle steering fault requirements comprising: receiving an input signal; dividing the input signal into a low frequency component and a high frequency component; limiting the low frequency component to a maximum value, to create a limited signal; and combining the limited signal and the high frequency component, to create a limited command signal.
A system for conforming an input signal to vehicle steering fault requirements comprising: an electric steering system generating an input signal in operable communication with a low pass filter configured to generate a low frequency component from the input signal. The input signal is also in operable communication with one of: a high pass filter to generate a high pass component and a first summing device in operable communication with said low pass filter to generate the high pass component. The system also includes a maximum value limiting device for limiting the low frequency component to a maximum value and to create a limited signal, the maximum value limiting device is in operable communication with the low pass filter. Additionally, the system includes a second summing device for combining the limited signal and the high frequency component to create a limited command signal, the signal summing device is in operable communication with the maximum value limiting device and one of, the high pass filter and the first summing device whichever generates the high pass component.
Also disclosed herein in an exemplary embodiment is a system for conforming an input signal to vehicle steering fault requirements comprising: a means for obtaining an input signal; a means for dividing the input signal into a low frequency component and a high frequency component; a means for limiting the low frequency component to a maximum value to create a limited signal; and a means for combining the limited signal and the high frequency component to create a limited command signal.
Also disclosed herein is a storage medium encoded with a machine-readable computer program code, the storage medium including instructions for causing a controller to implement the above-mentioned method for conforming an input signal to vehicle steering fault requirements.
Also disclosed herein is a computer data signal, said data signal comprising code configured to cause a controller to implement a method for conforming an input signal to vehicle steering fault requirements.
In a further disclosure herein of another exemplary embodiment, a method for conforming an input signal to fault requirements comprising: receiving an input signal; dividing the input signal into a low frequency component and a high frequency component; limiting the low frequency component to a maximum value, to create a limited signal; and combining the limited signal and the high frequency component, to create a limited command signal.
Moreover, also disclosed is a system for conforming an input signal to fault requirements comprising: an input signal in operable communication with a low pass filter configured to generate a low frequency component from the input signal. The input signal is also in operable communication with one of: a high pass filter to generate a high pass component and a first summing device in operable communication with said low pass filter to generate the high pass component. The system also includes a maximum value limiting device for limiting the low frequency component to a maximum value and to create a limited signal, the maximum value limiting device is in operable communication with the low pass filter. Additionally, the system includes a second summing device for combining the limited signal and the high frequency component to create a limited command signal, the signal summing device is in operable communication with the maximum value limiting device and one of, the high pass filter and the first summing device whichever generates the high pass component.
Further, disclosed herein in an exemplary embodiment is a system for conforming an input signal to fault requirements comprising: a means for obtaining an input signal; a means for dividing the input signal into a low frequency component and a high frequency component; a means for limiting the low frequency component to a maximum value to create a limited signal; and a means for combining the limited signal and the high frequency component to create a limited command signal.
Yet, another exemplary embodiment discloses a storage medium encoded with a machine-readable computer program code, the storage medium including instructions for causing a controller to implement the above-mentioned method for conforming an input signal to vehicle steering fault requirements.
Finally, disclosed herein is a computer data signal, said data signal comprising code configured to cause a controller to implement a method for conforming an input signal to vehicle steering fault requirements